Voltage regulator



Apfil 21, 1964 A. M. IOAKIMIDIS VOLTAGE REGULATOR Filed Jan. 11, 1960 Nx Ai United States Patent 3,130,361 VOLTAGE REGULATOR Anthony M. Ioakimidis, Chicago, Ill., assignor to International Telephone and Telegraph Corporation, a corporation of Maryland Filed Jan. 11, 1960, Ser. No. 1,709 6 Claims. (Cl. 323--22) This invention relates to power supplies and more particularly to voltage regulators for controlling such power supplies.

It is known to provide voltage regulators wherein a variable resistance is connected in series between a source of potential and a load circuit, the resistance being adjusted to compensate for fluctuations in the voltage across the load. A simple but relatively crude method of controlling the voltage is to provide a potentiometer and a volt-meter so that a person observing the volt-meter may adjust the potentiometer to maintain a substantially uniform voltage. A more sophisticated method is to provide an electronic device, which, analogously speaking, functions as an automatic variable resistor. One such method relates to voltage regulators wherein a reference potential is used to control a transistor that is connected in series between a source of potential and a load circuit. A problem that was not satisfactorily solved heretofore relates to the manner in which the reference potential applied to the transistor is maintained at a constant value.

Therefore, an object of the invention is to provide new and improved voltage regulators.

Another object of the invention is to provide selfcompensating voltage regulators which control voltage fluctuation with greater accuracy.

Yet another object of this invention is to provide transistorized voltage regulators having reference potentials which are automatically controlled to provide a greater degree of regulation.

In accordance with this invention, a voltage regulator system employs a pair of controllable semi-conductive devices connected to regulate automatically the voltage supplied from a direct cur-rent source to an electric load regardless of whether voltage variations encountered are due to changes of the load resistance, variations in the voltage supplied or combinations thereof. Improved regulation is accomplished by closer control of a reference potential that is applied to a control electrode of one of the semi-conductive devices which is in series with the load. The reference potential is controlled by the inter-action of the other semi-conductive device and a substantially constant potential device.

The above mentioned and other objects of this invention together with the manner of obtaining them will become more apparent and the invention itself will be best understood by making reference to the following description of an embodiment of this invention taken in conjunction with the accompanying single drawing which shows an electronic voltage regulator that is made in I accordance with the principles of the subject invention.

While the invention is described in connection with the preferred embodiment, it will be understood that the invention is not to be limited to the specific embodiment that is shown and described, and that the appended claims are intended to cover the various alternative and equivalent constructions which are included within the spirit and scope ofthe invention.

Turning now to the drawing, a source of AC. line voltage shown as transformer coupled to rectifying bridge 12 has filtering capacitor 17 connected across the output thereof. Between rectifying bridge 12 and electrical load circuit 15 there is shown a voltage regulator circuit including various resistances, P-N-P transistor Q1, and N-P-N transistor Q2, and .Zener diode 11. Transistor Q1 3,130,361 Patented Apr. 21, 1964 is in series with the load. Transistor Q2 and Zener diode 11 are connected across the DC voltage supply, and are combined with resistor 13' to form a non-linear voltage divider circuit. The base of transistor Q2 is connected via resistor 18 to the junction point B of resistor 16 and the collector of transistor Q1. The base of transistor Q1 is connected to junction point D of transistor Q2 and Zener diode 11, the potential at point D being used as a reference in controlling the voltage regulator.

The characteristics of N-P-N transistor Q2 are utilized in this circuit in conjunction with the voltage-current characteristics of Zener diode 1-1 to control any Zener voltage fluctuations. The reference voltage at point D and consequently at the base of P-N-P transistor Q1 is controlled as required to counteract load voltage variations resulting from fluctuations of voltage at the input terminal A of the regulator and/or fluctuations of the load current.

The Zener diode 11 is used primarily because the voltage drop between its terminals is fairly constant once it reaches a breakdown voltage despite relatively large fluctuations in current flow therethrough. However, it is to be noted that there are Zener voltage fluctuations which must be controlled.

The N-P-N transistor Q2 is used to control Zener voltage variations primarily by controlling the current flow through Zener diode 11.

When the circuit is first energized from source 10' both N-P-N transistor Q2 and Zener diode 111 are in an 01f condition. However, the potential which is applied from rectifier 12 across resistances 13, 14 and Zener diode 11 switches Zener diode 11 to its highly conductive state; whereupon, substantial current flows therethrough. With the Zener diode conducting, the potential which appears at point D becomes more positive and transistor Q2 turns on so that current flows between points A and D through transistor Q2.

The potential at point D is applied to the base of P-N-P transistor Q1 and controls the voltage at point C. Due to transistor characteristics, the emitter voltage (point C) approaches the base voltage (point D). That is, within a given current range, the voltage drop between points B and C varies as a function of the voltage applied at point A and the load current; however, Within the same current range, the voltage at point C varies as a function of the voltage at the base of transistor Q1. Therefore, the voltage at point C remains constant if the voltage which is applied to the base of transistor Q1 remains constant-within the given current range.

The voltage at the base of transistor Q1 is determined by the voltage at point D. Because of the Zener diode current-voltage characteristics, the voltage at point D depends on the current flow through Zener diode 11. That is, the voltage at point D tends to increase if the current flow through Zener diode 11 increases and tends to decrease if the current flow through Zener diode 11 decreases. Transistor Q2 controls the voltage at point D by controlling the current flow through Zener diode 11.

The current flow through transistor Q2 consists of the sum of the currents flowing through Zener diode 11 and flowing from the base of transistor Q1. Characteristically when the current flowing between points B and C increases, the current flowing from the base of transistor Q1 also increases. This increased current flow through transistor Q1 increases the voltage drop across transistor Q1. However, this increased voltage drop is cancelled because transistor Q2 is biased to allow greater current flow through Zener diode 11 when greater current flows between points B and C. The additional current flowing through Zener diode 11 increases the voltage at point D. In this way the base voltage of transistor Q1 is controlled to maintain a constant voltage across load 15 regardless of fluctuation of current flow, input voltage or combinations thereof.

It should be understood that there may be a variety of conditions which cause fluctuations in the voltages of the circuit shown in the drawing; however, it is thought that the circuit functions will be fully understood if two conditions are examined in detail; first assume a constant load and a variable voltage from rectifier 12 applied at point A and second, assume a constant output voltage from rectifier 12 applied at point A and a variable load current. A combination of these two conditions produces results similar to those described below but in varying degrees.

First, assume that the load current remains constant and that the voltage source varies in a manner which is such that point A becomes more negative. When point A becomes more negative, the voltage at point B also becomes more negative thereby making both the collector of P-N-P transistor Q1 and the base of N-P-N transistor Q2 more negative.

Assuming that transistor Q2 and associated components were not included in the circuit, when the voltage at point A increases, the voltage across resistor 13 and Zener diode 11 would also increase. Because of this increased voltage, the current through the Zener diode would increase as a function of the increased voltage. This increased current through Zener diode 11 would cause the voltage drop across Zener diode 11 to increase raising the potential at point D and consequently the potential at the base of transistor Q1. Since the emitter of a transistor follows the base, the voltage of the emitter of transistor Q1 would also increase thereby increasing the voltage across load 15.

With transistor Q2 in the circuit, and increased voltage at point A, there is no increase in current flow through Zener diode 11. That is, because the voltages at points A and B increase by the same amount, the bias voltage between the base and the emitter of transistor Q2 does not change. The bias voltage between the base and the emitter of a transistor controls the current through the transistor; therefore, the current through transistor Q2 does not change. Because the current through transistor Q2 does not change, there is no increase in the current through Zener diode 11 which is in series with the collector of transistor Q2. Since there is no change in the current through Zener diode 11, there is no change in the potential at point D. Therefore, there is no change in the potential at the base of transistor Q1. Since the volt age on the emitter follows the voltage on the base of a transistor, there is no change in voltage at point C which is the voltage across load 15.

Summarizing the action of the circuit when transistor Q2 is in the circuit and when there is an increase of voltage at point A: there is no current change in Zener diode 11 which is connected to the collector of transistor Q2 because the bias from emitter to base of transistor Q2 remains unchanged.

Next, assume that the current through the electrical load 15 increases and the voltage at point A remains the same. With the increased current in load 15, the voltage drop across resistance 16 increases and consequently the voltage at point B becomes more positive than what it was before in reference to the voltage at point A. If transistor Q2 were not in the circuit then the increased current flowing through transistor Q1 from emitter to collector inherently would mean an increased emitter to base current flowing from the transistor Q1. These increased currents would cause an increased voltage drop between the emitter and the base of transistor Q1. This voltage drop, along with the increased voltage drop across resistance 16, would cause the voltage at point C to decrease. The-voltage at point C would also decrease because the increased current would flow through resistor 13 from the base of transistor Q1. Since the voltage at point A is constant, any increased current flow through resistance 13 would cause an increase in voltage drop across resistance 13 which would cause a reduction in the current through Zener diode 11. Consequently, the voltage drop across Zener diode 11 would decrease. This would cause the voltage at point D to decrease and therefore the potential at the base of transistor Q1 would decrease. This would add to the decrease of potential at point C.

With transistor Q2 in the circuit the current through Zener diode 11 is increased. Since the emitter of transistor Q2 is connected through resistance 13 to point A, and further since the base of transistor Q2 is connected through resistance 18 to point B, base to emitter bias is provided by the voltage drop across resistance 16. Because of the increased load current and the consequent increased voltage drop across resistor 16, the potential at the base of transistor Q2 becomes more positive in relation to the potential at the emitter thereof. Therefore, N-P-N transistor Q2 draws more current. Since all of the current required by transistor Q2 cannot be supplied by the base current of transistor Q1 additional current is drawn through Zener diode 11. The increased current through Zener diode 11 causes the Zener potential to increase. The increased voltage drop across resistance 13 and Zener diode 11 which is caused by the increased current flow therethrough, is cancelled by a corresponding voltage drop across the collector and emitter of transistor Q2.

Summarizing the role of transistor Q2 when the load current is increased: transistor Q2 controls the current fiowing through Zener diode 11 thus controlling the voltage drop thereacross and maintaining a desired reference potential at point D.

An increased voltage at point D causes the base of transistor Q1 to be at a higher potential which compensates for the greater Voltage drop between the emitter and the base. Therefore the voltage at point C which is the voltage across load 15 remains constant.

Thus, it is seen that the circuit as shown in the drawing provides a regulated voltage across the load which is independent of fluctuations of voltage at point A and current through load 15.

In view of the inherent limitations of transistor Q1 it is apparent that the voltage regulator which is shown in the attached drawing has a limited power hnadling capacity. If it is necessary to increase the power which is delivered to load 15, additional transistors may be connected in parallel with transistor Q1.

While the principles of the invention have been described above in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of the invention.

1 claim:

1. A voltage regulator comprising a pair of transistors each having an electrode to control the voltage drop there-across, means including a first of said transistors for controlling the output voltage of a circuit extending from a power source to an electrical load, a nonlinear resistance, a voltage divider, said voltage divider comprising said nonlinear resistance in series with the other of said transistors, means in series with said first transistor and responsive to fluctuating load currents in said circuit for varying potentials applied to the control electrode of said other transistor, and means for connecting the electrode of said first transistor to said voltage divider to control said voltage fluctuations in said circuits.

2. A device for regulating the voltage across a load circuit comprising a power source including a direct current supply, a first semi-conductive device which conducts increased current responsive to control potentials of a first polarity, means for connecting said first semiconductive device in series in a circuit extending from said direct current supply to an electrical load circuit to control the fluctuations of voltages applied to said load, a second semi-conductive device which conducts increased current responsive to control potentials of an opposite polarity, means including a resistor in series with said first semi-conductive device and operated responsive to fluctuations in the voltage emanating from said direct current supply for controlling the current flow in said second semi-conductive device, and Zener diode means responsive to the operation of said last named means for controlling the output voltage of said first semi-conductive device whereby said semi-conductive devices provide compensating changes which cause the transmittal of substantially uniform voltage to said electrical load.

3. A device for regulating the voltage across a load circuit comprising means including a first semi-conductive device for controlling the output load voltage in a circuit extending from a power source to said load circuit, a nonlinear voltage divider having two segments, a component in one of said segments having a voltage drop which is substantially independent of variations in current flow therethrough, a second semi-conductive device in the other of said segments having current conducting characteristics which are substantially independent of variations of voltage supplied thereto, means shunting said second semiconductive device for switching said first semi-conductive device to its highly conductive state, means for connecting said voltage divider across said power source, and means responsive to potentials derived from said voltage divider for controlling the voltage output from said first semi-conductive device to compensate for the fluctuations in the output of said power source.

4. In a direct current voltage regulator for maintaining a load voltage independent of fluctuations in load current and fluctuations in supply voltage, the combination comprising: a DC. voltage supply, a load, a first semi-conductive device which conducts increased current responsive to an increase in negative control potentials, means for conmeeting said first semi-conductive device to control the output voltage in a circuit extending from said supply to said load, a second semi-conductive device which conducts increased current responsive to an increase in positive control potentials, a Zener diode, means including a resistor in series with said first semi-conductive device for connecting said second semi-conductive device and said Zener diode to provide a reference potential which is controlled as a function of fluctuations of said supply voltage and said load current, and means for coupling said Zener diode to said first semi-conductive device to control said first semi-conductive device to compensate for fluctuations in said supply voltage and fluctuations in said load current, whereby voltage across an electrical load is maintained constant.

5. In a voltage regulator for controlling direct current voltage, the combination comprising; a source of direct current, a load circuit, a P-N-P semi-conductive device and an N-P-N semi-conductive device, each having emitter, collector and base electrodes, means for connecting said source of direct current to said load circuit through the collector and emitter terminals of a first of said devices, a Zener diode, means for series connecting the collector and emitter terminals of the other of said devices and said Zener diode, means for connecting the base terminal of said other device to a circuit including said collector and emitter terminals of said first semi-conductive device, and means for connecting the base electrode of said first device to said series connection, whereby the complementary characteristics of said Zener diode and said N-P-N device cause mutually compensating changes to provide a substantially uniform voltage at an input of said load circuit.

6. A voltage regulator circuit comprising Zener diode means for obtaining reference potentials, means including a transistor with its control electrode coupled to a supply potential and responsive to circuit voltage and current variations for controlling said Zener diode means, means including a resistor in a series circuit connecting the supply to a load, and means responsive to said controlled reference potentials for maintaining a constant output voltage.

Designing Transistor Circuits-41C. Regulators, Richard B. Hurley, Electronic Equipment, April 1957, pp. 20-23. 

2. A DEVICE FOR REGULATING THE VOLTAGE ACROSS A LOAD CIRCUIT COMPRISING A POWER SOURCE INCLUDING A DIRECT CURRENT SUPPLY, A FIRST SEMI-CONDUCTIVE DEVICE WHICH CONDUCTS INCREASED CURRENT RESPONSIVE TO CONTROL POTENTIALS OF A FIRST POLARITY, MEANS FOR CONNECTING SAID FIRST SEMICONDUCTIVE DEVICE IN SERIES IN A CIRCUIT EXTENDING FROM SAID DIRECT CURRENT SUPPLY TO AN ELECTRICAL LOAD CIRCUIT TO CONTROL THE FLUCTUATIONS OF VOLTAGES APPLIED TO SAID LOAD, A SECOND SEMI-CONDUCTIVE DEVICE WHICH CONDUCTS INCREASED CURRENT RESPONSIVE TO CONTROL POTENTIALS OF AN OPPOSITE POLARITY, MEANS INCLUDING A RESISTOR IN SERIES WITH SAID FIRST SEMI-CONDUCTIVE DEVICE AND OPERATED RESPONSIVE TO FLUCTUATIONS IN THE VOLTAGE EMANATING FROM SAID DIRECT CURRENT SUPPLY FOR CONTROLLING THE CURRENT FLOW IN SAID SECOND SEMI-CONDUCTIVE DEVICE, AND ZENER DIODE MEANS RESPONSIVE TO THE OPERATION OF SAID LAST NAMED MEANS FOR CONTROLLING THE OUTPUT VOLTAGE OF SAID FIRST SEMI-CONDUCTIVE DEVICE WHEREBY SAID SEMI-CONDUCTIVE DEVICES PROVIDE COMPENSATING CHANGES WHICH CAUSE THE TRANSMITTAL OF SUBSTANTIALLY UNIFORM VOLTAGE TO SAID ELECTRICAL LOAD. 